Salad Cream is a product of First World War rationing. The classic ingredients of mayonnaise being in short supply, it became difficult to make enough mayonnaise to go round. Heinz were the first company to perfect an alternative blend of cheaper, more readily available ingredients.
It’s not a million miles from classic mayonnaise ingredients, but it does have a more ‘industrial’ recipe containing oil, water, egg yolks, vinegar, sugar, mustard, salt, thickeners, spices, flavourings and colourings.
Not generally available in the US until after the Millennium, British ex-pats in the US spread the word and now major supermarket chains carry it.
There are a host of rival concoctions from other manufacturers, but the exact taste and texture, like all Heinz products, is elusive to recreate.